IMPACT OF CLIMATE CHANGE ON THE HYDROLOGY OF UPPER BLUE NILE RIVER BASIN: A CASE STUDY IN TANA SUB-BASIN, ETHIOPIA

Abstract

Climate change is one of the serious issues in the word including developed and developing countries like Ethiopia. Tana Sub-Basin is located in the upper Blue Nile River basin . The aims of this study was to evaluate the impact of climate change on the hydrology of Upper Blue Nile River basin of Tana sub-basin in the northwest of Ethiopia. Dynamically downscaled climate model precipitation and temperature outputs were obtained from CORDEX-Africa program RCP4.5 and RCP8.5 by Regional Climate Model. The climate data has significant bias and bias correction was done by using CMhyd tool before used as input to the impact analysis. The analysis was performed in two future projection, 2020-2049 and 2050-2079 considering the reference baseline period 1988-2017 with both RCPs. Minimum temperature changes for RCP 4.5 raised by 0.26°C to 1.10°C and 0.45°C to 2.77°C, and for RCP8.5 0.15°C to 1.58°C and 1.02°C to 2.68°C Mean monthly minimum temperature change for 2020 – 2049 and 2050 – 2079. and Maximum temperature changes for RCP 4.5 and increase by 0.25°C to 1.6°C and 0.1°C to 1.91°C and for RCP 8.5 0.11°C to 1.92°C and 0.19°C to 2.17°C for 2020 – 2049 and 2050 – 2079 time periods with reference to the baseline periods respectively. And also, the mean monthly precipitation change will be increased and decreased by 2.09% to 23.95 % and 30.73% to 47.46% for both RCP4.5 and RCP8.5 scenarios respectively. The SWAT models were used to assess the streamflow response to climate change. Calibration and validation of the model output were performed by comparing simulated streamflow with observed flows from Tana Sub Basin (Blue Nile River outlet at Bahirdar gauging station) for the periods 1988-2001 for calibration and 2002-2008 for validation using SWAT-CUP(SUFI-2). The model calibration and validation result shows R2 and NSE of 0.87 and 0.84 and 0.61 and 0.6 during calibration and validation respectively. Finally, climate change impact on monthly streamflow was evaluated by relating base period stream flow with the future flows for the 2020-2049 and 2050- 2079 for both RCP4.5 and RCP8.5 scenarios. The future streamflow result shown increasing and decreasing change for both RCP4.5 and RCP8.5 scenarios. Hence, the increased and decreased stream flow in the basin may have a significant contribution for the sustainability of existed and undergoing water development projects